Located some 11 billion light-years from Earth are two clouds of gas. Just two billion years younger than the Big Bang itself, they appear to be the first known clouds that are completely unaltered since the birth of the universe.

The elements that make up a cloud of gas or other cosmic structure can help reveal when it originally formed. The very first nuclear reactions after the Big Bang only created the lightest elements: hydrogen, helium, and a tiny smattering of helium. All the heavier elements - which astronomers give the blanket term "metals", even those that aren't metallic in a chemical sense - were formed later, in the fiery crucibles of the early stars.

Now astronomers Michele Fumagalli and Xavier Prochaska at UC Santa Cruz and John O'Meara of St. Michael's College in Vermont have spotted two pristine clouds that are basically completely devoid of metals. Fumagalli explains what this means:

"Their chemical composition is unusual. This gas is of primordial composition, as it was produced during the first few minutes after the Big Bang."

The two clouds are located in the constellations of Leo and Ursa Major, which has given them their unofficial nicknames. The Leo Cloud is located 11.6 billion light-years from Earth, while the Ursa Major Cloud is even further out, at 11.9 light-years. That places both at a point roughly two billion years after the Big Bang. The clouds are located in front of even more distant quasars, and the powerful light from these ancient structures has helped illuminate the clouds.

Using the Keck I telescope at Mauna Kea, Hawaii, the researchers studied the composition of the clouds. They found plenty of hydrogen, but no other element. While the Keck I telescope isn't really suited to picking up the signatures of the other primordial elements, helium and lithium, it should have been able to detect the presence of heavier elements like oxygen or carbon. The fact that none were spotted strongly suggests the clouds formed before the first stars created these elements.

What's more, the astronomers say the hydrogen-to-metal ratio of the clouds is less than 1/6000 that of the Sun in the Leo Cloud and just 1/16000 in the Ursa Major Cloud. Even the most ancient stars in our galaxy have a ratio of at least 1/50 that of the Sun. The clouds also contain significant amounts of the hydrogen isotope deuterium, which astronomers believe was created in quantities after the Big Bang but destroyed during the formation of the stars. The researchers say this discovery should help fill in some vital questions about when ancient gas clouds began to contain metals, and how that fits into the larger evolution of the universe.